DESCRIPTION: This proposal represents an attempt to study the molecular basis of altered drug accumulation in cells overexpressing the P- glycoprotein (pGP). This proposal is aimed at evaluating the kinetic differences in drug translocation in cells expressing different levels of pGP generated either by selection in cytotoxic agents or co- selection in G418. Drug translocation will be monitored using fluorescent substrates (doxorubicin, coumarin-vinblastine, COL-FITC) by continuous monitoring of fluorescence. The studies will determine the importance of pHi and the electrical plasma membrane potential in the role of drug translocation and the role of pGP in the generation of these physiological parameters. These parameters will be characterized in cell lines expressing different amounts of pGP. pHi will be modulated by incubation in at different levels of C02 and extracellular HCO3 and membrane potential with ouabain and tri-ethyl-ammonium.